A telephone cord which connects a telephone handset to a telephone base generally comprises a polymeric core having a plurality of tinsel ribbons wrapped helically thereabout. These cords may have either a linear configuration or may be wound in a helical configuration comprising a plurality of convolutions, the latter being referred to as a retractile or spring cord. Telephone cords are well disclosed in the prior art such as, for example, U.S. Pat. No. 3,037,068 issued May 29, 1962 in the name of H. L. Wessel, and in U.S. Pat. Nos. 2,920,351 and 3,024,497 issued on Jan. 12, 1960 and Mar. 13, 1962 respectively in the names of E. C. Hardesty and D. L. Myers, all incorporated by reference hereinto.
In the past, tinsel conductors were covered with a nylon knit and then insulated with an extruded polyvinyl chloride (PVC) composition. A plurality of individually insulated conductors were jacketed with a plasticized PVC composition. See priorly mentioned U.S. Pat. No. 3,037,068.
In a somewhat recently introduced cord connection arrangement, which is referred to as modularity, miniature plugs are connected to each end of a line or spring cord to facilitate attachment to jacks in telephone instruments and in wall outlets. For example, see U.S. Pat. Nos. 3,699,498 and 3,761,869 issued Oct. 17, 1972 and Sept. 25, 1973 respectively in the names of E. C. Hardesty, C. L. Krumreich, A. E. Mulbarger, Jr. and S. W. Walden and in U.S. Pat. No. 4,148,359 issued Apr. 10, 1979 in the name of E. C. Hardesty, all incorporated by reference hereinto.
With the introduction of modularity, it became necessary to use a different cord construction because of a need for a smaller cross-section to be compatible with the plugs. In order to reduce the size of the insulated conductor, the plasticized nylon covering over the served tinsel was replaced with a crystalline thermoplastic elastomer as disclosed and claimed in U.S. Pat. No. 4,090,763 issued on May 23, 1978 in the names of W. I. Congdon, J. J. Mottine and W. C. Vesperman, which is incorporated by reference hereinto. A material such as that disclosed and claimed in the above-identified Congdon et al application is available commercially from E. I. duPont Company under the trade name HYTREL.RTM. polyester elastomer.
Typically, insulation over tinsel conductors is formed by an extrusion process which is referred to as tubing such as is disclosed, for example, in U.S. Pat. No. 3,553,042 issued on Jan. 5, 1971 in the name of E. R. Cocco and which is incorporated by reference hereinto. The tubing process provides that a plastic extrudate which is to form the insulation encloses but is spaced from the tinsel conductors to provide for relative movement therebetween, thus adding to the flexibility and to the life of the telephone cord. In a typical tubing operation, the downstream end of a core tube in an extruder crosshead is at least flush with or extends beyond the vicinity of a die opening.
The prior art also shows techniques for controlling the engagement of the tubed plastic extrudate with the core being enclosed. In U.S. Pat. No. 4,206,611, which issued on June 3, 1980 in the names of W. M. Kanotz, W. A. Lockhart, George F. Piper, W. C. Vesperman and M. K. Wilson and which is incorporated by reference hereinto, an extruded tubular covering is held out of contact with an advancing conductor until the extrudate becomes sufficiently form-sustaining by suitable crystallization. Then, when the crystallized insulation is drawn down on the conductor, any tinsel burrs which protrude outwardly are compressed. This results in a conductor having a continuously concentric insulation having a uniform wall thickness.
One problem that has surfaced during the use of HYTREL.RTM. plastic as an insulation cover relates to the extrusion process. The extruder which is shown in above-identified U.S. Pat. No. 4,206,611 includes a typical tubing arrangement in which the nose or free end of the core tube extends slightly beyond the die opening of the extruder crosshead. As the extrudate emerges from the die opening, prematurely crystallized portions of the plastic material which are called crystallites and which may have formed somewhere between the extruder screw and the die opening adhere to the surface of the conventional protruding or flush free end of the core tube. These small portions further crystallize, break off and form lumps in the conductor insulation or they may continue to accumulate and result in large masses adhered to the extruder tooling.